quantum condensed matter physics: organic insulators and...
TRANSCRIPT
Quantum condensed matter physics:organic insulators
and ultracold atoms
HARVARDsachdev.physics.harvard.eduWednesday, March 2, 2011
Outline
1. Organic insulators: antiferromagnets on the triangular lattice
2. Ultracold atoms: bosons in tilted Mott insulators
Wednesday, March 2, 2011
Outline
1. Organic insulators: antiferromagnets on the triangular lattice
2. Ultracold atoms: bosons in tilted Mott insulators
Wednesday, March 2, 2011
Half-filled band à Mott insulator with spin S = 1/2Triangular lattice of [Pd(dmit)2]2
à frustrated quantum spin system
X[Pd(dmit)2]2 Pd SC
X Pd(dmit)2
t’tt
Wednesday, March 2, 2011
H =�
�ij�
Jij�Si · �Sj + . . .
H = J
�
�ij�
�Si · �Sj ; �Si ⇒ spin operator with S = 1/2
Wednesday, March 2, 2011
Found in -(ET)2Cu[N(CN)2]Clκ
Anisotropic triangular lattice antiferromagnet
Classical ground state for small J’/J
Wednesday, March 2, 2011
Anisotropic triangular lattice antiferromagnet
Classical ground state for large J’/JFound in Cs2CuCl4
Wednesday, March 2, 2011
Valence bond solid
Anisotropic triangular lattice antiferromagnet
N. Read and S. Sachdev, Phys. Rev. Lett. 62, 1694 (1989)
=
Wednesday, March 2, 2011
Valence bond solid
Anisotropic triangular lattice antiferromagnet
N. Read and S. Sachdev, Phys. Rev. Lett. 62, 1694 (1989)
=
Wednesday, March 2, 2011
Valence bond solid
Anisotropic triangular lattice antiferromagnet
N. Read and S. Sachdev, Phys. Rev. Lett. 62, 1694 (1989)
=
Wednesday, March 2, 2011
Valence bond solid
Anisotropic triangular lattice antiferromagnet
N. Read and S. Sachdev, Phys. Rev. Lett. 62, 1694 (1989)
=
Wednesday, March 2, 2011
M. Tamura, A. Nakao and R. Kato, J. Phys. Soc. Japan 75, 093701 (2006)Y. Shimizu, H. Akimoto, H. Tsujii, A. Tajima, and R. Kato, Phys. Rev. Lett. 99, 256403 (2007)
Observation of a valence bond solid (VBS) in ETMe3P[Pd(dmit)2]2
Spin gap ~ 40 K J ~ 250 K
X-ray scattering
Wednesday, March 2, 2011
Magnetic Criticality
t’/t
T N (K
)
Magnetic order
Quantum critical
Spin gap
Me4P
Me4As
EtMe3As
Et2Me2As Me4Sb
Et2Me2P
EtMe3Sb
EtMe3Pt’/t = 1.05
Y. Shimizu, H. Akimoto, H. Tsujii, A. Tajima, and R. Kato, J. Phys.: Condens. Matter 19, 145240 (2007)
X[Pd(dmit)2]2Et2Me2Sb (CO)
VBS order
Wednesday, March 2, 2011
=
Triangular lattice antiferromagnet
Z2 spin liquid
P. Fazekas and P. W. Anderson, Philos. Mag. 30, 23 (1974).N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
Triangular lattice antiferromagnet
Z2 spin liquid
P. Fazekas and P. W. Anderson, Philos. Mag. 30, 23 (1974).N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
Triangular lattice antiferromagnet
Z2 spin liquid
P. Fazekas and P. W. Anderson, Philos. Mag. 30, 23 (1974).N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
Triangular lattice antiferromagnet
Z2 spin liquid
P. Fazekas and P. W. Anderson, Philos. Mag. 30, 23 (1974).N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
Triangular lattice antiferromagnet
Z2 spin liquid
P. Fazekas and P. W. Anderson, Philos. Mag. 30, 23 (1974).N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
Triangular lattice antiferromagnet
Z2 spin liquid
P. Fazekas and P. W. Anderson, Philos. Mag. 30, 23 (1974).N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
Triangular lattice antiferromagnet
Z2 spin liquid
P. Fazekas and P. W. Anderson, Philos. Mag. 30, 23 (1974).N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Candidate for aZ2 spin liquid:
κ-(ET)2Cu2(CN)3
Wednesday, March 2, 2011
=
-1
Excitations of the Z2 Spin liquid
A vison
N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
-1
Excitations of the Z2 Spin liquid
A vison
N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
-1
Excitations of the Z2 Spin liquid
A vison
N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
-1
Excitations of the Z2 Spin liquid
A vison
N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
-1
-1
Excitations of the Z2 Spin liquid
A vison
N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
=
-1
-1
Excitations of the Z2 Spin liquid
A vison
N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
• A characteristic property of a Z2 spin liquidis the presence of a spinon pair condensate
• A vison is an Abrikosov vortex in the paircondensate of spinons
• Visons are are the dark matter of spin liq-uids: they likely carry most of the energy,but are very hard to detect because they donot carry charge or spin.
Excitations of the Z2 Spin liquid
A vison
N. Read and S. Sachdev, Phys. Rev. Lett. 66, 1773 (1991)
Wednesday, March 2, 2011
Effective description of Z2 spin liquids, their visons and valence bond solids
Quantum dimer model:
D. Rokhsar and S. A. Kivelson, Phys. Rev. Lett. 61, 2376 (1988)R. Moessner and S. L. Sondhi, Phys. Rev. Lett. 86, 1881 (2001)
H =V
�����
�� �����+ V
�����
�� �����
− J
�����
�� �����− J
�����
�� �����
Hilbert space - set of dimer coverings of triangular/square lattice
Wednesday, March 2, 2011
Outline
1. Organic insulators: antiferromagnets on the triangular lattice
2. Ultracold atoms: bosons in tilted Mott insulators
Wednesday, March 2, 2011
Outline
1. Organic insulators: antiferromagnets on the triangular lattice
2. Ultracold atoms: bosons in tilted Mott insulators
Wednesday, March 2, 2011
SusannePielawa
TakuyaKitagawa
ErezBerg
S. Sachdev, K. Sengupta, and S.M. Girvin, Phys. Rev. B 66, 075128 (2002)S. Pielawa, T. Kitagawa, E. Berg, S. Sachdev, arXiv:1101.2897
Wednesday, March 2, 2011
M. Greiner, O. Mandel, T. Esslinger, T. W. Hänsch, and I. Bloch, Nature 415, 39 (2002).
Superfluid-insulator transition of 87Rb atoms in a magnetic trap and an optical lattice potential
Wednesday, March 2, 2011
M. Greiner, O. Mandel, T. Esslinger, T. W. Hänsch, and I. Bloch, Nature 415, 39 (2002).
Mott insulator of 87Rb atoms in a magnetic trap and an optical lattice potential
Wednesday, March 2, 2011
Applying an “electric” field to the Mott insulator
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Why is there a peak (and
not a threshold)
when E = U ?
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Resonant transition when E≈U
Wednesday, March 2, 2011
Virtual state
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Virtual state
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Resonant transition when E≈U
Wednesday, March 2, 2011
Resonant transition when E≈U
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Wednesday, March 2, 2011
Hamiltonian of resonant subspace
Wednesday, March 2, 2011
H = −√
2t
�
i
�d†i + di
�+ ∆
�
i
d†i di
∆ = U − E
Hamiltonian of resonant subspace
dipole
Wednesday, March 2, 2011
H = −√
2t
�
i
�d†i + di
�+ ∆
�
i
d†i di
∆ = U − E
Hamiltonian of resonant subspace
d†i di ≤ 1 d†i did†i+1di+1 = 0
no neighboring dipoles:max one dipole per site:Constraints:
dipole
Wednesday, March 2, 2011
H = −√
2t
�
i
�d†i + di
�+ ∆
�
i
d†i di
∆ = U − E
Hamiltonian of resonant subspace
d†i di ≤ 1 d†i did†i+1di+1 = 0
no neighboring dipoles:max one dipole per site:Constraints:
dipole
Wednesday, March 2, 2011
H = −√
2t
�
i
�d†i + di
�+ ∆
�
i
d†i di
∆ = U − E
Hamiltonian of resonant subspace
d†i di ≤ 1 d†i did†i+1di+1 = 0
no neighboring dipoles:max one dipole per site:Constraints:
dipole
Strong off-site quantum correlations
Wednesday, March 2, 2011
Phase diagram of dipole model
(E-U)/t
S. Sachdev, K. Sengupta, and S.M. Girvin, Phys. Rev. B 66, 075128 (2002)
Wednesday, March 2, 2011
(E-U)/tIsing quantum
phase transition
S. Sachdev, K. Sengupta, and S.M. Girvin, Phys. Rev. B 66, 075128 (2002)
Phase diagram of dipole model
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
SusannePielawa
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
SusannePielawa
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Strong tilt: maximize sites with 2 bosons
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Strong tilt: maximize sites with 2 bosons
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Strong tilt: maximize sites with 2 bosons
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Maximum number of 2’s
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Can also get some 3’s from neighboring 2’s.
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Can also get some 3’s from neighboring 2’s.
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Can also get some 3’s from neighboring 2’s.
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Can also get some 3’s from neighboring 2’s.
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Can also get some 3’s from neighboring 2’s.
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Can also get some 3’s from neighboring 2’s.
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Can also get some 3’s from neighboring 2’s.
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
No more 3’s are possible, but some 2’s are left over
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Start againWednesday, March 2, 2011
e
Tilting a decorated square lattice
Another maximal set of 2’sWednesday, March 2, 2011
e
Tilting a decorated square lattice
Maximum number of 3’s with no 2’s left over
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Configurations map onto dimer coverings of the square lattice !
SusannePielawa
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Go backwards around a plaquetteWednesday, March 2, 2011
e
Tilting a decorated square lattice
Go backwards around a plaquetteWednesday, March 2, 2011
e
Tilting a decorated square lattice
Go backwards around a plaquetteWednesday, March 2, 2011
e
Tilting a decorated square lattice
Go backwards around a plaquetteWednesday, March 2, 2011
e
Tilting a decorated square lattice
Then create a different set of 3’sWednesday, March 2, 2011
e
Tilting a decorated square lattice
Then create a different set of 3’sWednesday, March 2, 2011
e
Tilting a decorated square lattice
A different dimer coveringWednesday, March 2, 2011
e
Tilting a decorated square lattice
SusannePielawa
Dimers can resonate around a plaquette
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
Dimers can resonate around a plaquette
SusannePielawa
Wednesday, March 2, 2011
e
Tilting a decorated square lattice
SusannePielawa
Strong tilt: effective quantum dimer model
Wednesday, March 2, 2011
Many common issues on many body quantum correlations in condensed matter and ultracold atoms
Tilting Mott insulators can generate many interesting states with non-trivial quantum entanglement
Conclusions
Wednesday, March 2, 2011